DESCRIPTION (APPLICATION ABSTRACT): Orthopedic surgeons and physical therapists frequently assess outpatients with orthopedic problems for the presence of proximal deep vein thrombosis (PDVT), a relatively common and potentially life-threatening condition in these types of patients. No research has reported whether orthopedic surgeons and physical therapists correctly diagnose outpatients with PDVT. Given that PDVT is a relatively common condition, misdiagnosis of this condition could result in substantial mortality and morbidity as well as inefficient care. Recently published evidence indicates that use of a clinical prediction rule in combination with noninvasive diagnostic testing is the most effective approach for identifying patients with this potentially fatal condition. The primary aim of this study is to establish whether clinicians treating outpatients with orthopedic problems correctly estimate the probability of PDVT in patients with different amounts of risk for PDVT. The study will also examine whether these clinicians recommend the use of radiological/laboratory diagnostic tests in accordance with published research evidence. A survey methodology will be used to assess clinicians? approaches to the clinical examination and diagnosis of PDVT. A total of 2,500 orthopedic physical therapists and 2,500 orthopedic surgeons from their respective national organizations will be surveyed using stratified random sampling. Eight case simulations will be written for the survey. The case simulations will represent patients who have a predetermined probability of PDVT that varies from 3 to 75 percent according to a previously validated clinical prediction rule. A series of questions will be asked after each case. The questions will ask clinicians to estimate the probability of PDVT and to indicate which diagnostic tests, if any, the clinician might prescribe. The study will describe whether orthopedic surgeons and physical therapists accurately estimate the probability of PDVT in a variety of patients with orthopedic problems and the extent to which the use of diagnostic tests aligns with published evidence.